Evaluating lacustrine groundwater discharge to a large glacial lake using regional scale radon‐222 surveys and groundwater modelling

Abstract

Lacustrine groundwater discharge (LGD) can be an important pathway for delivering pollutants to lakes but this pathway is often poorly characterized. Evaluating the potential impact of LGD on lake water quality requires understanding the magnitude and spatial variability of LGD, as well as understanding the age and flow paths of the discharging groundwater (e.g., recharge area, groundwater flow paths, and travel times). This study first compares LGD rates along two $40 km shoreline lengths of a large glacial lake, Lake Simcoe, Canada, that were independently estimated via a radon-222 ( 222 Rn) field survey and via regional scale groundwater-surface water modelling. Backward particle tracking analysis is then used to examine the age and flow paths of the LGD and thereby assess the potential for the LGD to deliver anthropogenic pollutants to the lake. The field and modelling results compare well with respect to the magnitude and spatial variability ofLGD. However, the comparison highlights the need for well-defined hydrogeological characterization if regional scale models are to be applied for LGD estimation. The particle tracking analysis indicates large variation in the groundwater flow path lengths and travels times (>1000 years to <50 years) for LGD along the shoreline. This illustrates that the LGD along different shoreline areas has varying potential to deliver anthropogenic pollutants to the lake. The study findings demonstrate the benefits of comparing independent field measured and model-simulated LGD estimates, and moreover suggest that it may be possible, in some cases, to use existing regional scale groundwater-surface water models, purpose-built for other water resource and quality objectives, to conduct preliminary evaluation of LGD contributions to lakes. Preliminary model-based evaluation would enable field efforts aiming to quantify and manage LGD to be better targeted rather than relying solely on regional scale field techniques that are often highly resource intensive.

Spatial variability of lacustrine groundwater discharge in the largest urban lake in Asia: Coupled influence from land use and hydrogeology

“…In this study, the source terms of 222 Rn in the lake water are groundwater discharge and sediment diffusion, and the sink terms are self‐decay and atmospheric escape. Therefore, the 222 Rn mass balance model in this study can be expressed as (Imam et al, 2021; Shi et al, 2022; Wallace et al, 2021): $$$$ \frac{\partial {\mathrm{I}}^{222}\mathrm{Rn}}{\partial t}={F}_{\mathrm{LGD}}+{F}_{\mathrm{diff}}-{F}_{\mathrm{atm}}-{\mathrm{I}}^{222}\mathrm{Rn}\times {\lambda}^{222}\mathrm{Rn} $$$$ …”

“…In this study, the source terms of 222 Rn in the lake water are groundwater discharge and sediment diffusion, and the sink terms are self-decay and atmospheric escape. Therefore, the 222 Rn mass balance model in this study can be expressed as (Imam et al, 2021;Wallace et al, 2021): which occurs at the interface between lake water and sediments. F diff is a function of lake water temperature and sediment porosity, expressed by the following formula (Boudreau, 1996;Lee et al, 2012):…”

“…LGD has been quantified in various types of natural lakes, including oxbow lakes (Sun et al, 2022), glacial lakes (Luo et al, 2018; Wallace et al, 2021), giant saline lakes (Kong et al, 2021), deep great lakes (Schilling et al, 2016), and lacustrine pockmarks (Reusch et al, 2015; Wirth et al, 2020). However, LGD in changing environments, such as urban lakes, has received little attention.…”

Hydraulic Relationship between Hulun Lake and Cretaceous Confined Aquifer Using Hydrochemistry and Isotopic Data

“…Since precipitation is the initial input source of groundwater, it is of great significance to evaluate the isotopic characteristics of surface water and groundwater based on the atmospheric precipitation line. Firstly, based on the 2022 precipitation isotope of the Hulun Lake basin, a linear regression model was adopted to construct the atmospheric precipitation evaporation trend line (LMWL) for the analysis of the isotope characteristics [35]. The analysis of the δD and δ 18 O values of the water bodies in the basin (Figure 4 water and lake water, which causes the spatial distribution of the stable isotope composition [38].…”

Spatial Patterns and Quantification of Lacustrine Groundwater Discharge Determined Based on 222Rn

“…Previous studies on LGD have investigated various types of lakes, including small shallow lakes (Dimova et al., 2013; Schmidt et al., 2010), small deep stratified lakes (Meinikmann et al., 2013), deep great lakes (Liao et al., 2018; Schilling et al., 2016), tundra lakes (Dabrowski et al., 2020), and proglacial lakes (Luo et al., 2018; Wallace et al., 2021). However, there has been no specific study on groundwater discharge in oxbow lakes, a unique type of lakes that commonly feature deep channels and have important wetland ecological functions.…”